JP2974524B2 - Manufacturing method of ceramic coated steel sheet with excellent heat and corrosion resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a plated steel sheet having excellent heat resistance and corrosion resistance used for various parts of automobiles, building materials, home appliances and office equipment.

[0002]

2. Description of the Related Art The transition from post-coating to pre-coated steel sheets has been actively promoted. However, coated steel sheets have problems with welding and electrical products that require a thick conductive coating and grounding of electrical products. Will be used.) The quality of the post-treated plated steel sheet is highly dependent on the thickness of the organic film, and a quality that balances corrosion resistance and conductivity is required.

[0003] As a prior art disclosed as these post-treated plated steel sheets, there is Japanese Patent Application Laid-Open Publication No. Sho 57-108292 which discloses a steel sheet in which a coating made of chromate, SiO ₂ and resin is coated on zinc plating. Since this steel sheet uses an organic resin, there is a limit in heat resistance and wear resistance. Also,
If the resin film thickness is reduced to increase the conductivity, the corrosion resistance is reduced accordingly. Therefore, there is a limit to the conventional technology that uses resin as a main component for components that require further conductivity.

[0004]

SUMMARY OF THE INVENTION The present invention is to provide a post-treated steel sheet having excellent corrosion resistance, heat resistance, electrical conductivity and abrasion resistance, which was limited by conventional post-treated steel sheets. In the present invention, the constitution of the conventional resin film was developed with the idea of ensuring corrosion resistance with a thin film thickness, mainly composed of an inorganic ceramic. In general, ceramics are inferior in ductility, and there is a problem that workability is deteriorated when coated on a plated steel sheet, and it has been difficult to apply it as a film of a post-treated plated steel sheet. An object of the present invention is to develop a post-treated steel sheet in which the surface of a plated steel sheet subjected to a chromate treatment is coated with a thin ceramic having good processing adhesion and limited by a specific component, and exceeds the quality limit of a resin main component.

[0005]

The present invention advantageously solves the problems of the prior art, and the gist is as follows.

(1) As a first layer on the surface of a plated steel sheet,
After performing a chromate treatment of 5 to 100 mg / m ^{2 in} terms of r, the molar ratio of SiO ₂ / MxOy was 2 as the second layer.
A 1% aqueous solution having a pH of 7 to 11 is coated with a coating amount of 0.05 to 1.0 g / m ^{2 in} terms of SiO _2, and then heated to 80 to 300 ° C. as the ultimate plate temperature. For producing ceramic-coated galvanized steel sheet with excellent corrosion resistance.

(2) The heat resistance as described in (1) above, wherein M of SiO ₂ / MxOy is an alkali metal.
A method for producing ceramic-coated galvanized steel sheets with excellent corrosion resistance.

[0008]

The coating of the present invention is composed of three layers: plating / chromate / ceramic.

The present invention includes galvanized steel sheets including electroplating, hot-dip plating, vapor deposition, and thermal spray plating, and can be applied to Zn plating and Zn alloy plating, Al plating and Al alloy plated steel sheets as plating types.

[0010] The chromate serves to passivate the plating surface and provide corrosion resistance, and further serves to fix the ceramic by oxo bonding. For the chromate treatment, electrolytic chromate, etching chromate and coating type chromate can be applied. In the present invention, a post-wash type chromate which is hardly soluble in water and alkali is particularly desirable. Specifically, electrolytic chromate or etching chromate, in which water-soluble chromium is removed by washing with water after chromate, is optimal. The chromate that is easily dissolved is because Cr ions dissolve in the ceramic liquid during the application of the ceramic and uneven appearance and cohesive failure easily occur, so that it is difficult to obtain close contact workability. The amount of chromate attached is C
r is preferably 5 to 100 mg / m ² .

FIG. 1 shows a zinc-nickel alloy-plated steel sheet having a plating amount of 20 g / m ² , with CrO ₃ / H ₂ SO ₄ = 50/0.
After performing cathodic electrolysis in a 5 g / l aqueous solution, washing with water and forming a chromate film, an 8% aqueous solution of No. 1 water glass as SiO ₂ was exchanged for Na ⁺ with a cation exchange resin to obtain a pH = 1.
0.6 Create an aqueous solution of (a value of 1% solution), the 200 mg / m ² was applied as SiO ₂ with a roll coater plated steel sheet a chromate treatment, baked sheet temperature 0.99 ° C. immediately 600 ° C. oven for 4 shows the relationship between the amount of deposited Cr (horizontal axis) and the quality (vertical axis) of a sample prepared by cooling and drying.

The quality evaluation method and criteria are as follows.

1) Corrosion resistance: Salt spray test (JIS-Z-
2371), the time at which 5% white rust was generated was measured, and evaluated according to the following criteria.

72 hours (×) 200 hours (△) 500 hours (〇) 1000 hours (◎) 2) Heat resistance: The sample was heated in an electric furnace at 300 ° C. for 2 hours and evaluated by a salt spray test.

3) Adhesion workability: 1T / 180 ° bending at room temperature, visually evaluated after peeling off the tape.

Peeling (×) Whitening (△) Micro-cracking Slight (〇) No more (◎) As shown in the figure, the Cr adhesion amount is 40 to 80 mg / m ² , and the corrosion resistance, heat resistance and adhesion workability are all good. Quality. When the amount of Cr adhered is 20 mg / m ² or less, the corrosion resistance decreases, and when the amount of Cr adhered is 100 mg / m ² or more, the adhesion workability decreases.

The ceramic coating is a coating composed of an oxide represented by SiO ₂ and MxOy.

MxOy is Na ₂ O, K ₂ O, Li ₂ O,
B ₂ O ₃ , Al ₂ O ₃ , CrO ₃ , P ₂ O ₅ , MoO
₃ , MnO ₂ , SnO ₂ , and particularly, alkali metal oxides (Na ₂ O, K ₂ O, Li ₂ O) have the best performance balance, and may be used in combination with other oxides. it can.

FIG. 2 shows electrolytic chromate (Cr adhesion amount 40 m)
g / m ²⁾ and with water glass in the zinc-nickel alloy plated steel sheet was applied by ion-exchange, SiO ₂ / Na of a coated sample adhered amount 150 mg / m ² as SiO ₂ obtained by baking the sheet temperature 0.99 ° C. _It shows the relationship between the ₂ O molar ratio (horizontal axis) and the quality (vertical axis). Good quality was obtained at a molar ratio of 3 to 6. If the amount is less than 2 mol, the corrosion resistance and heat resistance are reduced, and if the molar ratio is 1, the coating is easily dissolved and the corrosion resistance cannot be obtained. When the molar ratio is 8 or more, the adhesion decreases. Therefore, a molar ratio of 2 or more is required, and a molar ratio of 3 to 6 is a desirable range.

FIG. 3 shows an electrolytic chromate treatment (Cr adhesion amount 4
0 mg / m ² ) A sample with a ceramic coating having a SiO ₂ / MxOy molar ratio of 3 to 8 was prepared on a zinc-nickel alloy-plated steel sheet (coating amount 20 g / m ² ) by the above-described method, and the ceramic adhesion amount (SiO ₂ equivalent, horizontal Axis) and quality.

Amount of ceramic adhered (SiO ₂ equivalent) 0.2
Good performance was exhibited in the range of 0.5 g / m ^{2 to} 0.5 g / m ² . SiO
_If it is less than 0.1 g / m _{2 in} terms of ² , corrosion resistance and heat resistance will be reduced. In terms of SiO ₂ 0.1 g / m ² greater adhesion workability is lowered.

Table 1 shows an electro-galvanized steel sheet having an etching chromate (Cr adhesion amount 50 mg / m ² ) (plating amount 4
0 g / m ² ) and an alkali metal (Li ₂ O, K ₂ O, Na ₂ O) ceramic having a SiO ₂ / MxOy molar ratio of 3
It is obtained by evaluating the iO ₂ terms 0.2 g / m ² coated specimen. The salt spray test takes 5% of the time to generate white rust.
Evaluation was made based on time (x) 150 hours (△) 200 hours (〇) 300 hours (◎)｝. All samples showed good corrosion resistance, heat resistance, and close contact workability.

[0023]

[Table 1]

The reason why excellent corrosion resistance can be obtained by the ceramic coating is to maintain a water and corrosion ion factor blocking effect of the ceramic and a pH environment in which the plated metal is inactive. That is, zinc is passivated at pH 7-11 and Al at 4-10. The pH of the ceramic aqueous solution of the present invention is 7
~ 11 is desirable. FIG. Reference numeral 4 denotes an aqueous zinc-coated steel sheet having an etching chromate (Cr adhesion amount of 50 mg / m ² ) and an aqueous solution having a different pH obtained by changing the SiO ₂ / Na ₂ O molar ratio to the plating amount (40 g / m ² ), and applying a sheet temperature of 250.
℃ the baked SiO ₂ equivalent coating weight 0.2 g / m ² is obtained by evaluating the performance of the coated sample. The horizontal axis is the pH of the 1% aqueous solution, and the vertical axis is the quality. The salt spray test score is 5% time to white rust generation 72 hours (x) 150 hours (△) 2
Evaluation was made for 00 hours (〇) and 300 hours (◎)｝. Heat resistance and adhesion workability were evaluated by the methods described above. The adhesion decreases from around pH 8 and peels off at pH 7. Corrosion resistance is pH1
In No. 3, white rust is generated in a short time. The samples obtained in the pH range of 9 to 11 exhibited good corrosion resistance, heat resistance, and close contact workability.

Table 2 shows that chromic acid / phosphoric acid = 10/10 g /
applying an aqueous solution of l, coated chromate dried to 70 ° C. (Cr coating weight 15 mg / m ²⁾ was 5% Al-Zn alloy coated steel sheet (coating weight 45 g / m ²⁾ to the SiO ₂ / Na
MxOy other than Na ₂ O shown in the table was added to an aqueous solution having a ₂ O molar ratio of 2, and an aqueous solution (1% solution pH) having a total SiO ₂ / MxOy ratio of 3 was defined as 0.1% of SiO ₂ .
It is a performance test result of a sample coated with ² g / m ^{2 and} baked to a plate temperature of 150 ° C. and cooled.

P ₂ O ₅ , B ₂ O ₃ , Li ₂ O, MoO ₃
Showed good results. Al ₂ O ₃ slightly deteriorated in corrosion resistance and adhesion workability.

The ceramic is coated by a roll coater (natural, reverse), a squeezing roll, an air knife, dipping, or mist, and then heated to a temperature of 80 to 300 ° C. in a heating furnace, a hot air furnace, an infrared baking furnace, induction heating, or the like. Bake. In the case of pure zinc plating, if the temperature is 300 ° C. or more, zinc alloys, the temperature is desirably 250 ° C. or less. If the temperature is lower than 80 ° C., the water resistance of the ceramic coating is insufficient, and the ceramic coating is liable to deteriorate during water cooling.

[0028]

[Table 2]

[0029]

According to the present invention, an inexpensive surface-treated steel sheet having excellent corrosion resistance, heat resistance and adhesion workability can be provided. In addition, the insoluble chromate and the ceramic coating do not substantially dissolve chromium and the ceramic itself is harmless,
It is an eco-friendly steel plate. Further, the film thickness is small and the conductivity is excellent. Not only heat resistance but also abrasion resistance, chemical resistance and a colorless and transparent film, which are characteristics of ceramics, provide a high-grade appearance.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optimal range of the amount of Cr attached according to the present invention.

FIG. 2 is a view showing a preferable SiO ₂ / MxOy ratio.

FIG. 3 is a diagram showing the relationship between the amount of adhered ceramic and the quality of the present invention.

FIG. 4 is a diagram showing the relationship between pH and quality of the ceramic aqueous solution of the present invention.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshitaka Kimura 1 Kimitsu, Kimitsu City Nippon Steel Corporation Kimitsu Works (58) Field surveyed (Int. Cl. ⁶ , DB name) C23C 28/00

Claims (2)

(57) [Claims] 1. A surface of a plated steel sheet is subjected to a chromate treatment of 5 to 100 mg / m ^{2 in} terms of Cr as a first layer, and then a 1% aqueous solution having a molar ratio of SiO ₂ / MxOy of 2 or more is formed as a second layer. after the pH is 0.05 to 1.0 g / m ² coating in terms of SiO ₂ adhesion amount of coating of 7-11, heat, characterized in that heating to 80 to 300 ° C. as a reaching plate temperature, excellent in corrosion resistance Manufacturing method of ceramic coated galvanized steel sheet. 2. The method according to claim 1, wherein M in SiO ₂ / MxOy is an alkali metal.